Debunking Sex Health: Does Weight Really Change Plan B’s Effectiveness?

Let's be real—sometimes life happens. Condoms break, pills get missed, or maybe there wasn't protection at all. Enter emergency contraception (EC), your backup plan for preventing pregnancy after unprotected sex. But if you've done any research, you might have heard some concerning things about whether emergency contraception works as well for people with higher body weights.

So what's the truth? Does emergency contraception have weight limits? And what options do you have if you're worried? Let's dig into what the science actually says and what it means for your reproductive health.

The Weight Concern: Where It All Started

The conversation about emergency contraception and weight kicked into high gear in 2011 when researchers in Scotland discovered something concerning: Plan B (which contains levonorgestrel) seemed to fail more often in women with higher BMIs. This sparked plenty of questions and even more studies—with some mixed results.

Here's what research has found:

• Some studies suggest Plan B may become less effective for people weighing more than 155 pounds
• At weights above 175-176 pounds, its effectiveness might decrease more significantly
• This matters because the average weight of reproductive-age women in the US is around 168 pounds

While this sounds alarming, it's important to understand a few things: the evidence isn't crystal clear, the pills still provide significant protection against pregnancy for everyone, and there are other options available.

Why Would Weight Matter?

The science behind why weight might affect emergency contraception isn't completely understood, but there are some theories:

• Drug distribution: In higher body weights, the medication might become more diluted throughout your body
• Metabolism differences: Your body may process the hormones differently based on your weight
• Hormone interactions: Extra estrogen stored in body fat might interact with the medication

When contraception was first developed, it was a one-size-fits-all model. But our population now has evolved and is very different from the population when the drugs were first developed.

[Find the perfect emergency contraception for you →] Connect with Twentyeight Health provider who'll help you navigate your options

What Are Your Options?

First, remember this: no matter your weight, taking emergency contraception is better than taking nothing at all. 

Even studies showing reduced effectiveness still found pregnancy rates below 3% for Plan B users across all weight categories.

That said, if you weigh more than 155 pounds, here are your best options for emergency contraception:

1. Ella (Ulipristal Acetate)

• Effectiveness: Works better than Plan B for people with higher weights (up to about 195 pounds)
• Timing: Can be taken up to 5 days after unprotected sex (vs. 3 days for Plan B)
• Access: Requires a prescription, but you can often get this through telehealth services
• Pro tip: Consider asking your provider for an advance prescription to keep on hand

2. Copper IUD (Paragard)

• Effectiveness: Over 99% effective regardless of weight
• Timing: Can be inserted up to 5 days after unprotected sex
• Bonus: Provides ongoing contraception for up to 12 years
• Consideration: Requires a provider appointment, which can be hard to schedule quickly

3. Plan B (Levonorgestrel)

• Still an option: Even if you're above the weight threshold, it still reduces pregnancy risk
• Accessibility: Available over-the-counter without a prescription
• Timing: Works best within 72 hours of unprotected sex, sooner is better

[Unsure if Plan B is right for you? ]→ Chat with one of our providers who’ll listen to your unique needs 

What About Taking Extra Plan B?

You might be wondering: "Can I just take two doses of Plan B if I'm over the weight limit?"

A 2023 study specifically looked at whether doubling the dose of Plan B would help in people with BMIs over 30. Unfortunately, they found no significant difference in effectiveness between single and double doses. While taking two doses isn't considered unsafe, there's currently no evidence it improves the effectiveness.

Making the Decision: A Real Talk Moment

If you need emergency contraception and have concerns about your weight:

• Consider Ella first: if you can get a prescription quickly (our telehealth providers can provide prescriptions and ship them right to your door)
• Consider a copper IUD: if you can get an appointment within 5 days and are open to a longer-term contraception option
• Take Plan B: if the other options aren't available—it still significantly reduces pregnancy risk compared to doing nothing
• Act quickly: regardless of which option you choose—sooner is always better with emergency contraception

Beyond The Emergency: Looking Forward

If you've found yourself needing emergency contraception, this might be a good moment to think about your regular birth control method too. At Twentyeight Health, we can help you find a contraceptive that fits your body, lifestyle, and preferences—all without judgment.

[Talk to a provider about your options →]

Your reproductive health matters, no matter your size, and you deserve accurate information and effective options. Emergency contraception is never a guarantee against pregnancy, but it's an important tool that can significantly reduce your risk.

This article was medically reviewed by Twentyeight Health's clinical team.